I am assuming you are using v3.1 SR4
starting on line #813 of post.asp
You will see this code:
if strRqMethod = "Reply" or _
strRqMethod = "Edit" or _
strRqMethod = "ReplyQuote" or _
strRqMethod = "Topic" or _
strRqMethod = "TopicQuote" then
%>
<input name="Preview" type="button" value=" Preview " onclick="OpenPreview()">
Just add this line in there also: (either right before or right after "Topic" would probably be best)
strRqMethod = "EditTopic" or _